Ferrocene-containing monomers

ABSTRACT

1. A POLYMERIZABLE MONOMER SELECTED FROM PENTAERYTHRITOL METHACRYLATE TRIS (FERROCENOATE) AND PENTAERYTHRITOL ACRYLATE TRIS (FERROCENOATE).

United States Patent Otfice 3,847,958 Patented Nov. 12, 1974 3,847,958 FERROCENE-CONTAINING MONOMERS Travis E. Stevens and Samuel F. Reed, .lr., Huntsville,

Ala., assignors to the United States of America as represented by the Secretary of the Army No Drawing. Original application July 31, 1969, Ser. No. 849,254. Divided and this application May 18, 1971, Ser. No. 144,283

Int. Cl. C07f 15/02 US. Cl. 260439 CY 3 Claims ABSTRACT OF THE DISCLOSURE The ferrocene-containing polymerizable monomers, pentaerythritol methacrylate tris (ferrocenoate) and pentaerythritol acrylate tris (ferrocenoate), are disclosed along with the pertinent preparative procedures therefor. The specified ferrocene-containing monomers when copolyrnerized with butadiene serve as the propellant binder and catalyst for fast-burning composite propellants. The copolymers perform the functions of binder and catalyst in a propellant composition containing ammonium perchlorate, a plasticizer, and aluminum metal fuel.

CROSS REFERENCE TO RELATED APPLICATION This is a division of application Ser. No. 849,254, filed July 31, 1969.

BACKGROUND OF THE INVENTION Prior art compounds resulting from the selective partial esterification of pentaerythritol are known. Two derivatives of pentaerythritol which serve as the starting compounds for the preparation of the ferrocene containing monomers of this invention are pentaerythritol arsenite methacrylate and pentaerythritol arsenite acrylate.

The term polymerizable monomer is well known. The term when applied to the propellant art generally means a compound useful in propellants because it is capable of forming an elastic tough rubbery polymer by condensation or polymerization reactions in the propellant mix. The resulting rubbery polymer functions as a binder for the propellant charge. The binder provides strength for the propellant charge or grain. Many of the prior art compounds have been concerned with binder materials. The present trend has been to increase the performance of propellants by employing an energetic binder material, improved oxidizer, and burning rate catalyst.

The prior art esters of polymerizable compounds have been employed as energetic binder materials having oxidizing and plasticizing capabilities. The term energetic binder is a term to distinguish one type of binder from another type of binder known as non-energetic binder. The non-energetic binders provide binding functions while contributing little, if any, to the propellent burning processes. The propellant burning process is a complex process requiring a proper balance of fuel, oxidizer, and catalysts. The oxygen content of a number of energetic binders of the prior art enables those binders to contribute to the oxidizing capability of the propellant composition in addition to the binding capability of the propellant composition. Each active ingredient in a propellant composition contributes to one or more functions of the propellant system. Naturally, a multifunctional ingredient offers distinct advantages.

Generally, a burning rate additive has been required for use in the prior art propellant compositions to obtain increased burning rates. These additives or catalysts have included metallic oxides and organo-metallic compounds. Ferrocene and n-butyl ferrocene have been utilized as burning rate catalysts. The liquid ferrocene compounds have been eifective in promoting burning rates. However,

like all liquids used as additives, the characteristic disadvantages of liquid additives such as loss by evaporation, migration, etc., have caused processing problems as well as problems encountered later during long term storage of propellants.

An additive which is not subject to the disadvantages of some of the prior art compounds would be attractive for use in propellants.

The present invention has as its principal object to provide ferrocene-containing monomers which can be polymerized to form an energetic binder having a burning rate catalyst as an integral part thereof.

Another object is to provide copolymerization products of ferrocene-containing monomers and butadiene which serves as energetic binder and burning rate catalyst for propellant compositions.

A further object of this invention is to provide a propellant composition having a combination energetic binder and catalyst which does not evaporate during propellant processing or migrate in the finished propellant.

SUMMARY OF THE INVENTION The ferrocene-containing monomers, pentaerythritol methacrylate tris (ferrocenoate) and pentaerythritol acrylate tris (ferrocenoate) are produced from pentaerythritol arsenite methacrylate and pentaerythritol arsenite acrylate respectively as the starting compounds. The monomers become constituents of copolymers of butadiene when polymerization reaction is initiated by a suitable initiator. The copolymers of this invention are useful as binders for solid propellants which also contain an oxidiz/er, metal fuel, and plasticizer. The binders also func tion as a burning rate catalyst since the catalyst is an integral part thereof. The catalyst being an integral part of the cured binder does not migrate during propellant storage. The catalyst is evenly and widely dispersed as an integral part of the binder; therefore, this arrangement is conducive to uniform burning rate control and stability to burning of the propellant composition.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The starting compound, pentaerythritol arsenite methacrylate, forms one of the monomers of this invention and may be produced as follows:

To a clear solution of 10.4 grams (0.050 mole) of pentaerythritol arsenite in 20 milliliters of acetonitrile and 8 milliliters of triethylamine is added dropwise a mixture of 5.5 g. (0.052 mole) of methacryloyl chloride and 5 ml. of acetonitrile. The addition requires about 15 minutes while the temperature is maintained at about 35 C. to about 40 C. by external cooling. The mixture is stirred at 50 C. for two hours, then the solvent is removed at reduced pressure, and the residue is dried at ambient temperature and 1 millimeter of pressure for 30 minutes. The residue is extracted with three ml. portions of hot ligroin (each containing 5 mg. of hydroquinone). The extracts are concentrated and chilled and the product removed by filtration. The solid obtained is recrystallized from ligroin to give 5.40 grams of the monomer, pentaerythritol arsenite methacrylate, mp. 83 C. to 84.5 C.

Another starting compound, pentaerythritol arsenite acrylate, forms another monomer and may be produced as follows:

T o a mixture of 10.4 g. (0.050 mole) of pentaerythritol arensite and 10 ml. of acetonitrile is added 4.5 ml. (0.065 mole) of acrylic acid followed by 24 ml. (0.175 mole) of triethylamine. When the exotherm from the addition of the amine (the reaction temperature should not be allowed to exceed 20 C.) is subsided, 7.7 ml. (0.060 mole) of benzene-sulfonyl chloride in 10 ml. of acetonitrile is added, overa 15 minute p.erio d.,.The reaction mixture is cooled to keep the temperature below 30 C. during the addition; after the benzenesulfonyl chloride addition, the mixture is stirred at 30 C. for one hour.- The solvent is then removed at reduced pressure and the from methanol. The yield is pentaerythritol acrylate tris (ferrocenoate), 1.05 g., m.p. 107-109 C.

Analysis.Calculated for C H Fe C, 59.60; H, 4.64; Fe, 20.3. Found: C, 59.1; H, 4.59; Fe, 19.7.

residue dried at. ambient temperature and 1 millimeter of EXAMPLE HI pressure for 30 minutes. The residue is extragted three; c l i ti Wi h B t di times with 200 ml. of hot ligroin containing .01 g. o hydroquinone. The residue is taken up in methylene chlogg; gg g i i lg g i igfg gg gg g gfi i 'de and a ain stri ed to dryness. Recrystallization from I} g h 1 10 (2-methyl-S-hydroxy-v-aleronrtnle) as initiator, and 2.1 g. ligroln yields the rr onomer, pentaeryt rito arseni e acry- (0.0025 mole) pentaerythritol methacrylate my late 'P' 80 cm 82 f d (ferrocenoate). The reactor is attached to a vacuum 'Pentaeryihntol methacrylate ms errocenoate) an line and deaerated by three alternate freeze-thaw cycles. pentaerythritol acrylate ms (ferrocenoate) are mono- Butadiene (10.8 g. 0.2'mo1e) is condensed into the remers which are prepared as forth herembelow under actor, and the reactor transferred to an oil bath at 66- Examp I Speclfied E when 93' 67 C. Heating is continued for a period of 72 hours. P 89 wlth Putadlene .form t p On cooling the solvent is removed by evaporation and addmon to the binder functlol} ca the copolymer reprecipitated by dissolving in ether folfor the progenalit System wherem use Exanflp e H an lowed by the addition of methanol. After decanting the Example are luustranve of theprocequres otrflprepantl' 20 solvents, the copolymer is stripped of excess solvents on of h copolymers of this mveptlon' e I a rotatory evaporator and finally dried at 7075 C. under forth burnmg ratesof uncured composite prope dants usingI reduced pressure (1 mm.) for a period of 24 hours. The the hydrox.y termmated copolymer of bum an yield of liquid copolymer is 7.1 g. (55% The copolymer pentaerythritol methacrylaie ms (feriocenoate) con}- is characterized by molecular weight (3 500) OH end pared with a propellant using unmodified hydroxy-termi- 25 groups (121 wt percent) and elemental analysis (Fe nated polybutadiene, and a propellant using n-butyl Found, 3 ferrocene, a standard burning-rate promoter. Similarly, EXAMPLE IV the copolymer of pentaerythritol acrylate tris (ferrocenoa e) and. butadiene m y be used as t binder a cata- In a similar reaction to that set forth in Example III, lyst for a propellant composition. 5.4 g. (0.1) butadiene is copolymerized with 2.1 g. (0.0025 mole) of pentaerythritol methacrylate tris EXAMPLE I (ferrocenoate) in toluene with 0.756 g. (0.003 mole) azo- Preparation of,Penraerythntr01 Methaclfylate bis-(2-methyl-5-hydroxy-valeronitrile) as initiator to give TFIS (felfocenoate) 4.2 g. (56%) of the copolymer analyzing as follows: A 2.20 g. 8 mole) sample of pentaerythritol arsenite as molecular Weight end g p weight methacrylate and 20 mg. of dicyanobenzoquinone is P and elm6nta1 analysis Found stirred With 25 ml. of acetone and 6 ml. of waterv for Asnoted 111 P 1H IV the 111016 ratlO 0f 30 minutes at C. The solution is filtered, and'the butadlene to monomer 15 from about 40 to 1 to l the filtrate is stripped to dryness. The residue, in methylene 80 to 1 for morlomer The mole Tatlo 1n chloride, is dried over calcium sulfate. The solution is 40 Examples In W15 also satlfactory when the 3 again stripped to dryness, and the residue taken up in mer pentaerythrltol acrylate tris (ferrocenoate) 1s se- 8 ml. methylene chloride and 8 ml. of chlorobenzene. lectefi for copolymer preparatlon- This solution is added to 8.44 g. of ferrocenoyl chloride in 18 ml. of chlorobenzene in a. flask maintained at 200 Burmng Rate Data mm. pressure. When addition is complete, the pressure is 40 The hydroxy-terminated copolymer of butadiene and reduced to 150 mm. and the temperature is maintained at pentaerythritol methacrylate tris-(ferrocenoate) contain- C. for 1 hour. The chlorobenzene is removed in vacuo ing 39% F (prepolymer A f T bl 1), provides a and the residue is partitioned between methylene chloride significant increase in propellant burning rate. Table I and water. The organic residue is chromatographed on at below summarizes the data as compared with the standards silica gel column packed in pentane-methylene chloride 50 set forth therein. (2:1 and 1:1), and m hy n Chloride gives a Center Cut Similarly, the hydroxy-terminated copolymer of butaof 1.69 g. This portion is recrystallized from methanol diene and pentaerythritol acrylate tris (ferrocenoate) may to give pentaerythritol methacrylate tris (ferrocenoate), be used in place of the prepolymer, butadiene and 1.14 g., mp. 109-112 C. pentaerythritol methacrylate tris (ferroceno ate).

TABLE I Burning rates of uncured composite propellants Percent Rb at Prepolymer Plasticizer NH4C1O4 Al Additive 750 psi. 1,500 psi.

HTPB, 10 Isodecyl 70 1o 0. 54 0. s4

pelargonate.

do 70 10 0. 71 0. e7 70 10 NBF; 2... 0.71 0.97

1 Unmodified hydroxy-terminated polybutadiene. 2 n-Butyl ferrocene, a. standard burning-rate promoter.

Analysis-Calculated for C H Fe O C, 60.0; H, 4.80; Fe, 19.94. Found: C, 59.7; H, 4.80; Fe, 20.9.

EXAMPLE II Preparation of Pentaerythritol Acrylate tris (ferrocenoate) The procedure outlined in Example I above is followed using 1.71 g. of pentaerythritol monoacrylate (prepared by hydrolysis of pentaerythritol arsenite acrylate) and 10 g. of ferrocenoyl chloride. The organic residue obtained Isodecyl pelargonate is available under the trademark, Emolein from Emery Industries, Inc. Other suitable plasticizers include diisooctyl azelate, di-Z-ethylhexyl azelate, and dipropylene glycol dipelargonate.

The plasticizers noted above may be used with the copolymers of this invention in amounts from about 5 to about 25 weight percent of the propellant composition. The ammonium perchlorate may vary from about 50 to about 70 weigh percent of the propellant composition. The copolymers of this invention may be used in propelupon evaporation of the organic solvents is re-crystallized 75 lant compos tions in amounts from about 5 to about 30 weight percent. Aluminum metal from about 5 to about 20 weight percent may be used in the propellant composition containing the copolymers of this invention.

The copolymers of this invention may be substituted for polybutadiene and the burning rate catalyst employed in a propellant composition since the copolymers contain a catalyst as an integral part thereof. The copolymers of this invention are particularly attractive as a source of catalysis for the propellant composition in order to avoid the problems associated with the use of liquid catalysts (e.g. problems, such as, loss by evaporation or migration within the propellant during storage).

We claim:

1. A polymerizable monomer selected from pentaerythritol methacrylate tris (ferrocenoate) and pentaery- 15 thritol acrylate tris (ferrocenoate).

2. A polymerizable monomer of claim 1 and wherein said monomer is pentaerythritol methacrylate tris (ferrocenoate) 3. A polymerizable monomer of claim 1 and wherein LELAND A. SEBASTIAN, Primary Examiner US. Cl. XrR. 149-19.2 

1. A POLYMERIZABLE MONOMER SELECTED FROM PENTAERYTHRITOL METHACRYLATE TRIS (FERROCENOATE) AND PENTAERYTHRITOL ACRYLATE TRIS (FERROCENOATE). 